From the title of the issue: “Form-associated custom elements”. They are talking about the mechanism by which a custom element can have its value included when

From the title of the issue: “Form-associated custom elements”. They are talking about the mechanism by which a custom element can have its value included when you submit a form. Here’s the spec.: https://html.spec.whatwg.org/multipage/custom-elements.html#form-associated-custom-element https://html.spec.whatwg.org/multipage/custom-elements.html#... https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#association-of-controls-and-forms https://html.spec.whatwg.org/multipage/form-control-infrastr... https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#constructing-form-data-set https://html.spec.whatwg.org/multipage/form-control-infrastr...